Cellular solids are highly porous space filling materials with periodic or random microstructures. The effective properties of cellular solids are sensitive to the geometry of the underlying microstructures and the properties of the basis material from which these microstructures are made. In man-made cellular solids, the control of the microstructural geometry and the basis material properties is one of the key challenges in manufacturing. Foamed cellular solids typically feature a random microstructure of foam cells which is usually characterized through poor weight specific mechanical performance. For flat panel type of structures, cellular solids can be placed between two face sheets to form a sandwich panel. In particular, honeycomb sandwich panels are known for excellent bending stiffness to weight ratio. However, it appears to be impossible to manufacture metallic honeycombs in a cost-effective mass production process. Uni-directionally corrugated microstructures such as the core layer in cardboard can be produced very cost effectively. However, their weight specific mechanical performance is usually inferior to that of honeycombs. In particular, when used in metal sandwich construction, the bonding land between the core structure and the face sheets is often too small to transmit the full shear force through an adhesive bond. In other words, delamination between the core structure and the face sheets is often the critical failure mode. Furthermore, their mechanical properties are direction-dependent featuring a pronounced strong and weak direction when subject to transverse shear loading. In addition, the bonding land between a uni-directionally corrugated core structure and the face sheets is rather small and not well defined. Delamination is therefore a concern when using these materials for primary load carrying structures. It would thus be desirable to provide a technique for increasing the size of the bonding land without sacrificing weight specific mechanical performance. Uni-directionally corrugated core structures are the premier choice in applications such as packaging where costs are more important than strength and stiffness. It is apparent that it would be desirable to provide a man-made core structure which high weight specific strength and stiffness and which can be produced cost-efficiently. Anticlastic core structures as presented by Hale (1960) are equally strong in two perpendicular directions. Hale proposes various methods for making the anticlastic core structure from sheets. However, the applicability of Hale's invention seems to be limited to highly formable materials such as thermoplastics. When using conventional sheet metal, premature fracture typically limits the making of anticlastic structures (FIG. 1). It would thus be desirable to provide the geometry of forming tools which can be used to make anticlastic core structures from sheet metal. More specifically, it would be desirable to provide the geometry of forming tools which can be used for the mass production of large sandwich panels.
The procedures proposed by Hale require forces which are very large (as compared to the capacity of state-of-the-art presses) when used in conjunction with sheet metal. The procedures are thus limited to the production of small panels. It is desirable to provide a method which can be used for the production of large panels (such as needed for trucks).